The present invention relates in general to semiconductor power device technology, and in particular to structures and methods for forming a monolithically integrated trench gate field effect transistor (FET) and Schottky diode.
In today's electronic devices a power FET is often used in power conversion applications such as DC-DC converters. For many years, a Schottky diode was implemented external to the FET switch package to reduce power consumption. As shown in FIG. 1, FET 101 includes an internal diode 102 commonly referred to as body diode. During switching operations, the body diode can conduct current. As shown in FIG. 1, Schottky diode 104 is in parallel with body diode 102 of FET 101. Because a Schottky diode has lower forward voltage than the body diode, Schottky diode 104 turns on before body diode 102 turns on thus improving switching losses.
More recently, some manufacturers have introduced products in which discrete Schottky diodes are co-packaged with discrete power FET devices. There have also been monolithic implementations of power FETs with Schottky diode. An example of a conventional monolithically integrated trench FET and Schottky diode is shown in FIG. 2. A Schottky diode 210 is formed between two trenches 200-3 and 200-4 surrounded by trench FET cells on either side. N-type substrate 202 forms the cathode terminal of Schottky diode 210 as well as the drain terminal of the trench FET. Conductive layer 218 provides the diode anode terminal and also serves as the source interconnect layer for FET cells. The gate electrode in trenches 200-1, 200-2, 200-3, 200-4 and 200-5 are connected together in a third dimension and are therefore similarly driven. The trench FET cells further include body regions 208 with source region 212 and heavy body regions 214 therein.
The Schottky diodes in FIG. 2 are interspersed between trench FET cells. As a result, the Schottky diodes can consume a significant portion of the active area, resulting in lower current ratings or a large die size. This can be undesirable in certain device applications. There is therefore a need for a monolithically and densely integrated Schottky diode and trench gate FET with superior performance characteristics.